An X-ray photography system is known as one of industrial nondestructive inspection devices. For example, an X-ray inspection device having a micro-focus X-ray tube is used for inspection of electronic devices represented by semiconductor integrated circuit substrates. An X-ray tube is an X-ray source that emits an X-ray from a target by applying, between an anode and a cathode, a high voltage with a predetermined potential difference in accordance with an X-ray energy to irradiate the target with electrons accelerated by the high voltage. A micro-focus X-ray tube is an X-ray tube having a plurality of grid electrodes on the cathode side and has a function of converging the orbit of an electron beam by controlling an electrostatic lens with the voltage applied to these grid electrodes.
In an X-ray generating device using a micro-focus X-ray tube, improvement of a grounding scheme of the X-ray tube, a supplying method of a control signal, or the like has been made to address the need for controlling the voltage applied to the grid electrodes. For example, an X-ray generating device disclosed in Japanese Patent Application Publication No. 2003-317996 is configured such that the control signal of the grid voltage applied to grid electrodes is supplied through an optical fiber cable, and thereby a negative high voltage can be applied to the cathode of the X-ray tube. Further, a neutral grounding scheme in which an enclosure of the X-ray tube is grounded and a positive high voltage and a negative high voltage are applied to the anode and the cathode is employed, and thereby the voltage applied between the enclosure and the anode is reduced by around half.
In terms of easy handling or the like when installing an X-ray generating device in an X-ray photography system, there is a demand for a reduction in size of the X-ray generating device. Further, in terms of a higher penetrating power, there is a demand for an increase in the voltage applied to an X-ray tube. However, study by the inventors of the present application has first revealed that an advancement of reduction in size of the X-ray generating device or increase in the application voltage may increase malfunction of a control system.